Large printed vinyl sheets have generally replaced pasted paper signs in the outdoor advertising industry. Installation of large printed vinyl display sheets requires two or more workers who push light weight fiberglass or similar non-conductive rods through pockets heat-sealed in each of the four end surfaces of a sheet, which forms the advertising or display face of a billboard.
The vinyl sheets typically have to be hung from the top of a billboard after the top rods are secured to the billboard frame and then pulled or tensioned horizontally and vertically across the metal backing of the billboard. Various tensioning devices have been used. Generally the installation process requires at least two workers who take on average approximately 20 to 30 minutes or more to complete an installation.
The industry recently developed light weight vinyl or polyethylene display sheets, which can be recycled and cost less but are not as strong as the vinyl in predominate use today. Its lighter weight and lesser strength make the light weight vinyl or polyethylene display sheets unsuitable for heat-sealing pockets and more subject to tearing from excess tensioning and repeated installations and removals. Display sheets are frequently moved from one billboard location to another to save on printing and material costs.
U.S. Pat. No. 6,789,295 discloses a clamp apparatus for application to a plate, sheet, fabric or thin film by gripping two opposite sides of the object. A rope or cord is inserted into holes in the top and bottom units comprising the clamp apparatus. The rope or cord is secured to a stationary object. There is no accommodation for attachment to a cable, although each individual rope or cord could be tied to a cable. However, uniform tension to the display sheet can only be realized if the length of each piece of rope or cord running from each clamp apparatus around the perimeter of the display is identical. If the clamp apparatus is attached directly to the cable with the cable running through the holes in the top and bottom units, the clamp apparatus would be turned approximately 90 degrees to the face of the billboard or display surface, resulting in undesirable twists, folds, and wrinkles in the display sheet.
International Patent Publication No. WO 03/098055 issued to Gunnarsson discloses a clamp apparatus closely similar to the apparatus disclosed in U.S. Pat. No. 6,789,295. The clamp apparatus disclosed in the International Publication has the same deficiencies of U.S. Pat. No. 6,789,295 described above.
U.S. Pat. No. 4,686,748 issued to Kaivanto discloses an attachment device for gripping the edge of a sheet, but does not disclose a mechanism for removably attaching the device directly to a portion of a cable while the cable is under tension. The clamping mechanism squeezes the edge of a sheet or fabric between the curved edges of one unit and the tapered length of a second unit resulting in distortion, folding, or creasing of the sheet or fabric. This is an undesirable result for a billboard or other application where a flat display sheet is preferred. Additionally, the eyelet/rope combination of this attachment device would permit the display sheet to twist. As noted above, unless uniform lengths of rope or cord were used to attach the several clamps to a tension cable, uneven force would be applied to the display sheet resulting in folds, wrinkles, or other distortions of the display sheet.
It would be desirable to have a clip which could attach to a cable running horizontally and vertically along the perimeter of a billboard or display surface, which will minimize or eliminate twisting and wrinkling of the display sheet. It would be further desirable to have a clip which would allow application to a cable running parallel to the face of the clip and which clip would remain attached to the cable while one display sheet is removed and another installed in its place. It would be further desirable to have a clip that could be retained on the cable when a sheet is being dismounted, remounted or when the clip is not in use so that the clip is not dropped or lost. It would be further desirable to have a two-piece clip which will allow for limited movement of the two pieces with respect to each other when a sheet is detached from the clip yet prevent complete separation of the two pieces.
Kaivanto and Gunnersson disclose clips which require removal from the cable in order to become disengaged from the display sheet. To remove the sheet you have to remove the pressure. With Kaivanto, the bottom plate would fall off. It would be desirable to have a clip which could be retained on the cable during sheet changeout.